I used to have that modem (is it a Billion 7800 range?) and you might actually be able to squeeze a bit more speed out of your line by manually adjusting the SNR down to 3 or 4. You'd need to Google your exact modem to find out, its accessed via a hidden page (usually /snr.cgi) but the values you enter to adjust depends on your model.

Be careful though, your mileage may vary and it can make your connection unstable if you drop it too low. If it's unstable you can return it to its default values.

Using that method I managed to get an extra 40-50% sync speed, but my speeds were much worse than yours to begin with.